One of the most effective therapies for sleep apnea syndrome is nasal continuous positive airway pressure (CPAP) therapy, which adopts respiratory equipment that supplies gas at about 400 to about 2000 Pa positive pressure to the nasal cavity of a user during sleeping. In addition, one of the most effective therapies for ventilatory insufficiency is nasal intermittent positive pressure ventilation (NIPPV) therapy, which adopts respiratory equipment that intermittently supplies gas at about 400 to about 2400 Pa positive pressure to the nasal cavity of a user.
In cases of performing therapy using such equipment, in order to persistently supply positive-pressure gas to the nasal cavity of a user, there is used a nasal mask system composed of a hose to lead positive-pressure gas, a nasal respiratory mask, a frame to hold the nasal respiratory mask at a predetermined position, and a headgear to attach the nasal respiratory mask tightly to the face. The headgear comprises a headgear strap with an adjustable length and is connected to the frame through the headgear strap. The headgear strap makes it possible to adjust the tightness of contact between the nasal mask system and the face so that leakage of the positive-pressure gas can be almost eliminated without causing pain. Common means for keeping the length as it is include Velcro (registered trademark), a belt buckle, and the like. Generally, the nasal mask system is not worn when treatment is not administered. When the nasal mask system is taken off, the headgear strap is drawn out from the mask system. Accordingly, the length must be adjusted every time the mask is worn. In a common-nasal mask system, in order to compensate for this disadvantage, the length adjustment function is separated from the connection function to a frame in such a way that the headgear strap is connected to a fastener, the frame is provided with a fastener catch, and the fastener and the fastener catch share the function of connection/disconnection between the headgear and the frame. This nasal mask system dispenses with need for adjustment of the length upon re-wearing of the system.
Regarding methods for the connection between the headgear and the frame in these nasal mask systems, there have been disclosed various nasal mask systems adopting general technology and specific technology since operations for the connection are required to be performed nearby the nose in many cases.
For example, Patent Document 1 proposes a nasal respiratory mask system in which insertion of a fastener is aided by sliding the fastener in an in-plane direction on a guide plane of a fastener catch provided to a frame, and Patent Document 2 proposes a nasal mask system comprising a rotation mechanism to eliminate torsion of a headgear. These nasal respiratory mask systems are effective to some extent for improving operability upon wearing.
However, in these nasal respiratory mask systems, connection of a fastener may sometimes fail when the fastener is going to be inserted in a fastener catch while deviated in a rotating direction around the axis of the direction of insertion.
In addition, for correcting torsion of a headgear after wearing, a fastener must be composed of two or more parts, causing concern over an increase in total weight of the nasal mask system. In addition, there is also concern that the torsion might be still retained if the degree of freedom of rotation is 180 degrees or more in both directions.
Moreover, the headgear is usually washed on a daily basis and resin parts such as a fastener are disconnected at the time of washing. Since these parts are disconnected from a headgear strap portion at that time, the length must be adjusted every time after washing and it becomes difficult to readily attain a stable wearing condition. In addition, since the headgear strap generally has a structure in which the length is adjusted with Velcro (registered trademark) or the like, more frequent adjustment of the length accelerates deterioration of the headgear strap, significantly reducing the lifetime of the headgear. This problem is more serious for nasal respiratory mask systems lacking a connection/disconnection mechanism using a fastener and a fastener catch.
However, no consideration has been given to these points in existing techniques represented by those described above.
Patent Document 1: Japanese Patent Application Laid-open No. 2005-537903
Patent Document 2: Japanese Patent Laid-open Publication No. 2004-000572